This invention relates to an alignment system and more particularly to such a system for aligning a stamp/template parallel to a substrate surface for conformal contact.
Temporarily bringing two surfaces into physical contact with each other is required during several manufacturing processes. For example, during imprinting-based transfer of patterns from a stamp/template onto a substrate surface, the template must make conformal contact with the substrate. Conformal contact means that the entire surface of the template is in contact with the substrate; this contact ensures that pattern transfer is successful over the entire surface of the template. Conformal contact is hindered, however, by the initial angular misalignment between surfaces. This initial angular misalignment is illustrated in FIGS. 1(a) and 1(b). Note that stamp 10 is misaligned by angles θx and θy with a glass slide 12 so that the two surfaces are initially not parallel to each other. FIGS. 1(c) and 1(d) show front and side views after the stamp 10 and slide 12 are aligned by the method of the invention disclosed herein.
When soft/deformable templates are used, conformal contact may be achieved by compressing the template onto the substrate. However, this technique is not appropriate when the template contains fragile features that are susceptible to damage at high contact forces. An example of fragile features susceptible to damage includes DNA or metallic nanowires. Thus, to ensure conformal contact between such fragile surfaces one must (i) align the surfaces parallel to each other and (ii) maintain the contact forces below a threshold value. Although high precision stages are available for actively aligning surfaces at low contact forces, these stages are impractical for adoption in a manufacturing system because of their higher costs.
Currently available alignment stages can be divided broadly into two types based on their motion control system: (i) active alignment systems that use force and/or displacement feedback to perform alignment and (ii) passive systems that rely on the compliance of a soft/deformable stamp to achieve conformal contact. A six-axis nanopositioning motion stage is an example of an active system. A manual contact printing technique is an example of a passive system.
The advantage of an active alignment system is that fragile surfaces can be reliably aligned at low contact forces. However, such systems are difficult to scale-up due to the expensive, complex, and bulky sensors and actuators that are required for feedback motion control. This limitation is particularly critical when the templates are much smaller than the alignment system. For example, for biomedical applications it is more desirable to imprint-individual stamps/templates of size approximately 1 cm2 than to dice-up a large 6-8 inch wafer into smaller chips after imprinting. Scale-up would then involve introducing a precision stage of size approximately a few cubic feet for each stamp. This implementation is not practical for a manufacturing environment.
The advantage of a passive alignment scheme is that it eliminates the need for expensive sensors and actuators that are necessary for feedback control of an active motion system. Such passive alignment reduces the cost, complexity and size of the alignment, system. Although passive alignment may be easily achieved by manually guiding the surfaces to be aligned, such schemes have limited capability to provide a predetermined repeatable motion and to restrict the contact forces during alignment. In this case, conformal contact is achieved via compression/deformation of the template and relies on the compliance of the template. Thus, such systems are not appropriate for aligning surfaces that have fragile micro- and nano-scale features that may be damaged at high contact forces.
The present invention has particular application to imprinting of DNA nanowires. Details of such an application are found in “An Automated Stage for Scalable Imprinting of DNA Nanowires Based on a Self-aligning Technique,” Proc. ASME IMECE2012, the contents of which are incorporated herein by reference.
It is an object of the present invention to provide a tool to passively align two initially misaligned planar surfaces parallel to each other such that conformal contact is achieved and the contact forces are low. The passive alignment scheme according to the invention eliminates the need for expensive sensors and actuators for a motion system thereby lowering the cost of the alignment process by a factor of approximately one-hundred. The cost savings make it economical to adopt the present invention for large scale imprinting-based manufacturing.